Variable Displacement Compressor

ABSTRACT

Overpressure of refrigerant in a refrigerant circuit is avoided. A swash plate type variable displacement compressor includes a muffler (muffler space  123 ) at the top of a cylinder block  101  thereof. The muffler space  123  is connected to a communication passage communicating with a discharge chamber of the compressor, and in this connecting portion, a check valve  200  for suppressing a backflow of the refrigerant is provided. The muffler space  123  communicates with a discharge-side external refrigerant circuit via a discharge port. An inlet port of the high-pressure relief valve  250  in the muffler space  123  communicates with the muffler space  123  located on downstream side of the check valve  200 , and an outlet port thereof communicates with a crank chamber  105  of the compressor through communication passages  101   c  and  101   d  of the cylinder block  101 . The crank chamber  105  communicates with a suction chamber of the compressor through a gas bleeding passage. The high-pressure relief valve  250  is opened when pressure in the muffler space  123  increases to overpressure to flow refrigerant at a high pressure into the crank space  105  from the muffler space  123  through the communication chambers  101   c  and  101   d.

TECHNICAL FIELD

The present invention relates to a variable displacement compressor used in particular for in a vehicle air conditioning system.

BACKGROUND ART

Patent Document 1 discloses providing a relief valve in a communication passage communicating a discharge chamber with a crank chamber, and opening the relief valve when pressure in the discharge chamber exceeds a predetermined value, in a swash plate type variable displacement compressor constituting a refrigerant circuit.

Patent Document 2 discloses providing a check valve in a high pressure passage between a condenser and a discharge chamber of a compressor, and providing a relief valve at the upstream of the check valve in the high pressure passage, in a refrigerant circuit with a swash plate type variable displacement compressor.

CITATION LIST Patent Document

-   Patent Document 1: Japanese Laid-Open Patent Application Publication     No. 2002-61571 -   Patent Document 2: Japanese Laid-Open Patent Application Publication     No. H10-253174

SUMMARY OF INVENTION Problems to be Solved by the Invention

However, in a state in which the compressor constituting the vehicle air conditioning system is in operation and the vehicle air conditioning system including a condenser fun and a refrigerant circuit, when abnormality of a condenser fun occurs and when clogging occurs in the refrigerant circuit, in the refrigerant circuit, pressure on a region (discharge pressure region) on which discharge pressure of the compressor acts may increase to overpressure. In this situation, it has been customary to uncouple an electromagnetic clutch coupled to a driving shaft of the compressor, or to decrease a discharge quantity of the compressor to a minimum discharge quantity so as to drop the pressure on the discharge pressure region, thereby avoiding the occurrence of the overpressure on the discharge pressure region.

In this respect, the relief valve disclosed in Patent Documents 1 and 2 is under the necessity of avoiding the occurrence of the overpressure on the discharge pressure region by mechanically operating the relief valve, even if it fails to perform electrical control of the relief valve as mentioned above.

In the technique disclosed in Patent Document 1, it is possible to discharge the refrigerant in the discharge pressure region into the crank chamber without discharging the refrigerant into the air, even when the pressure on the discharge pressure region increases to the overpressure.

However, some variable displacement compressors used for in a vehicle air conditioning system include a check valve in a discharge pressure region, as is disclosed in Patent Document 2.

Applying the technique disclosed in Patent Document 1 to the variable displacement compressor equipped with the check valve in the discharge pressure region avoids the occurrence of the overpressure in the discharge chamber, but it results in closing the check valve with the pressure drop in the discharge chamber. Thus, there is a possibility of maintaining, at high pressure, the pressure on the discharge pressure region located downstream of the check valve.

In view of the aforementioned problems, an object of the present invention is to provide a variable displacement compressor equipped with a check valve able to avoid the occurrence of overpressure in a vehicle air conditioning system without discharging refrigerant in a discharge pressure region into the air, when pressure on the discharge pressure region increases to overpressure.

Means for Solving the Problems

In order to achieve the object, a variable displacement compressor according to the present invention includes a housing including a plurality of cylinder bores formed in parallel with one another around a shaft, a crank chamber provided at the front thereof, a suction chamber and a discharge chamber provided at the rear thereof, a discharge passage connecting the discharge chamber to a discharge-side external refrigerant circuit, and a suction passage connecting the suction chamber to a suction-side external refrigerant circuit; a piston inserted into the cylinder bore to reciprocate therein and compressing refrigerant drawn from the suction chamber to discharge the refrigerant into the discharge chamber; a driving shaft rotatably supported in the housing; a conversion mechanism including a swash plate of which inclination is changeable, the swash plate being arranged in the crank chamber and converting a rotary motion of the driving shaft into a reciprocating motion of the piston; and a displacement control valve changing the inclination of the swash plate by controlling pressure in the crank chamber to change a stroke of the reciprocating motion of the piston, in which the housing includes a first pressure release passage branched from the discharge chamber and connected to the crank chamber, and a second pressure release passage connecting the crank chamber to the suction chamber, in which a check valve which suppresses a backward flow of the refrigerant from the discharge-side external refrigerant circuit to the discharge chamber is provided in the discharge passage on an upstream side of a branching position at which the first pressure release passage branches off, and in which a high-pressure relief valve which opens the first pressure release passage when pressure in the discharge passage on a downstream side of the check valve exceeds a predetermined value is provided in the first pressure release passage.

Effects of the Invention

According to the present invention, since when the pressure on the region located on the downstream side of the check valve in the discharge passage exceeds the predetermined value, the first pressure release passage is opened by the high-pressure relief valve and high pressure refrigerant is discharged into the crank chamber through the first pressure release passage, the invention prevents the refrigerant from being discharged into the air during depressurization.

Furthermore, according to the present invention, when the pressure on the region located on the downstream side of the check valve in the discharge passage exceeds the predetermined value, the refrigerant in the region is discharged into the crank chamber through the first pressure release passage. Thus, the pressure in the crank chamber is suddenly increased and a discharge quantity of the variable displacement compressor is instantaneously changed to a minimum discharge quantity, to thereby markedly drop the pressure in the discharge chamber. Therefore, the invention enables avoiding the occurrence of overpressure in the discharge chamber.

Moreover, according to the present invention, when the pressure, for example, in a discharge-side external refrigerant circuit increases to the overpressure, further providing the second pressure release passage allows smooth migration of the high pressure refrigerant to the suction chamber through the discharge passage on the downstream side of the check valve, the high-pressure relief valve, the first pressure release passage, the crank chamber, and the second pressure release passage. Therefore, the invention also enables avoiding the occurrence of the overpressure in the discharge-side external refrigerant circuit.

Consequently, according to the present invention, since both the occurrence of the overpressure in the discharge chamber (that is, on the upstream side of the check valve in the discharge pressure region) of the variable displacement compressor, and the occurrence of the overpressure in the discharge-side external refrigerant circuit (that is, on the downstream side of the check valve in the discharge pressure region) are avoided, the invention enables enhancing the reliability of the vehicle air conditioning system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing a variable displacement compressor according to a first embodiment of the present invention;

FIG. 2 is cross-sectional view of a principle part showing a variable displacement compressor according to the first embodiment;

FIG. 3 is a cross-sectional view showing a high-pressure relief valve according to the first embodiment;

FIG. 4 is a cross-sectional view showing a variable displacement compressor according to a second embodiment of the present invention;

FIG. 5 is a cross-sectional view showing a low-pressure relief valve according to the second embodiment;

FIG. 6 is a cross-sectional view of a principle part showing a variable displacement compressor according to a third embodiment of the present invention;

FIG. 7 is a cross-sectional view showing a high-pressure relief valve according to the third embodiment; and

FIG. 8 is a cross-sectional view of a principle part showing a variable displacement compressor according to a fourth embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, descriptions will be made to embodiments of the present invention with reference to the accompanying drawings.

FIG. 1 schematically shows a structure of a variable displacement compressor according to a first embodiment of the present invention.

A variable displacement compressor 100 used for in a vehicle air conditioning system includes a cylinder block 101, a front housing 102 provided at one end of the cylinder block 101, and a cylinder head 104 provided at the other end of the cylinder block 101 via a valve plate 103.

In the cylinder block 101, a plurality of cylinder bores 101 a are formed in parallel with one another around a shaft (around a driving shaft 106).

A driving shaft 106 is provided so as to traverse the inside of a crank chamber 105, which is defined by the cylinder block 101 and the front housing 102 and positioned ahead of the cylinder bore 101 a. A swash plate 107 is arranged around the center of the driving shaft 106. The swash plate 107 is coupled to a rotor 108 fixed to the driving shaft 106 via a coupling part 109, and tiltably supported by the driving shaft 106. A coil spring 110 urging the swash plate 107 toward minimum inclination is attached between the rotor 108 and the swash plate 107. Similarly, a coil spring 111 urging the swash plate 107 toward a direction in which inclination of the swash plate 107 increases is attached at the opposite side bridging over the swash plate 107.

One end of the driving shaft 106 extends to the outside passing through the inside of a boss 102 a protruded outwards beyond the front housing 102, and is coupled to a power transmission device (not shown). Herein, power is transmitted from an external driving source (not shown) to the power transmission device. A shaft seal 112 is inserted between the driving shaft 106 and the boss 102 a, and the shaft seal 112 separates the inside of the variable displacement compressor 100 from the outside. The driving shaft 106 is supported by bearings 113, 114, 115, and 116 in radial and thrust directions and is rotatable in synchronization with rotation of the aforementioned power transmission device.

A piston 117 is inserted into the cylinder bore 101 a, and a circumference of the periphery of the swash plate 107 is received in a cavity 117 a formed in one end of the inside of the piston 117, the piston 117 and the swash plate 107 operate together via a shoe 118. Therefore, rotating the driving shaft 106 allows the piston 117 to reciprocate in the cylinder bore 101 a. Herein, a function of a conversion mechanism according to the present invention is implemented by the swash plate 107, the rotor 108, a coupling part 109, coil springs 110 and 111, and the shoe 118.

A suction chamber 119 is provided at the center of the cylinder head 104. Furthermore, a discharge chamber 120 is provided so as to annularly surround a suction chamber 119. In other words, the discharge chamber 120 is annularly arranged in the cylinder head 104 radially outward of the suction chamber 119. Herein, the suction chamber 119 and the discharge chamber 120 are positioned at the rear of the cylinder bore 101 a.

The suction chamber 119 communicates with the cylinder bore 101 a through a communication hole 103 a formed in the valve plate 103 and a suction valve (not shown).

The discharge chamber 120 communicates with the cylinder bore 101 a through a discharge valve (not shown) and the communication hole 103 b formed in the valve plate 103.

The piston 117 reciprocating in the cylinder bore 101 a compresses refrigerant (for example, refrigerant gas) drawn from the suction chamber 119 and discharges it into the discharge chamber 120.

The front housing 102, the cylinder block 101, the valve plate 103, and cylinder head 104 are fastened to form the housing by a plurality of through bolts 140 via a gasket (not shown). That is, the housing according to the present invention includes the front housing 102, the cylinder block 101, the valve plate 103, and the cylinder head 104.

At the top of the cylinder block 101, a muffler 121 having an extended space is provided for reducing noises and vibrations due to pulsations of the refrigerant.

The muffler 121 is provided by fastening with a bolt via a seal member (not shown) a formed wall 101 b vertically arranged on an upper surface of the cylinder block 101 and a box-shaped lid member 122 of which lower surface is opened and is a part of the aforementioned housing. Herein, the formed wall 101 b corresponds to “a volume part formed by providing a concavity on an outer surface of the cylinder block” according to the present invention. The lid member 122 covers an opening of the volume part.

At the upper end of the lid member 122, a discharge port 122 a communicating with the inside and the outside of the muffler 121 is formed.

A check valve 200 is arranged in a muffler space 123 that is a space (that is, the aforementioned extended space) in the muffler 121.

The check valve 200 is arranged at a connecting portion at which a communication passage 124 communicating with the discharge chamber 120 and the muffler space 123 are connected. The check valve 200 operates in response to a pressure difference between the communication passage 124 (upstream side) and the muffler space 123 (downstream side). When the pressure difference is smaller than a predetermined value, the check valve 200 closes the communication passage 124. In contrast, when the pressure difference is greater than the predetermined value, the check valve 200 opens the communication passage 124. Herein, the predetermined value is a threshold value for switching open and close operations of the check valve 200, which is previously set so as to suppress a backward flow of the refrigerant from the muffler space 123 (downstream side) to the communication passage 124 (upstream side).

Thus, the discharge chamber 120 is connected to a discharge-side refrigerant circuit (discharge-side external refrigerant circuit of the present invention) of the vehicle air conditioning system through a discharge passage including the communication passage 124, the check valve 200, the muffler space 123, and the discharge port 122 a. Furthermore, the check valve 200 suppresses a backward flow of the refrigerant from the discharge-side refrigerant circuit to the discharge chamber 120.

In the cylinder head 104, a suction port 104 a and a communication passage 104 b communicating with the suction port 104 a and the suction chamber 119 are formed.

Therefore, the suction chamber 119 is connected to the suction-side refrigerant circuit (suction-side external refrigerant circuit of the present invention) of the vehicle air conditioning system through a suction passage including the suction port 104 a and the communication passage 104 b.

In the cylinder head 104, a displacement control valve 300 is provided.

The displacement control valve 300 regulates an opening of a gas supplying passage 125 communicating with the discharge chamber 120 and the crank chamber 105 to control a discharge refrigerant introduction amount to the crank chamber 105. Moreover, the refrigerant in the crank chamber 105 flows into the suction chamber 119 through a gas bleeding passage 128. Here, in the gas bleeding passage 128, the refrigerant in the crank chamber 105 passes through a gap between the bearings 115 and 116 and the driving shaft 106, and goes through a space 127 formed in the cylinder block 101 and an orifice 103 c formed in the valve plate 103.

Hence, by regulating the discharge refrigerant introduction amount to the crank chamber 105 to change the pressure in the crank chamber 105 by the displacement control valve 300, followed by changing inclination of the swash plate 107 to change a stroke of reciprocating motion of the piston 117, a discharge quantity of the variable displacement compressor 100 is controlled. In this connection, the displacement control valve 300 is an external control displacement control valve operating in response to an external signal. More specifically, the displacement control valve 300 detects pressure in the suction chamber 119 through a communication passage 126 communicating with the suction chamber 119, and regulates an amount of electric current to a solenoid of the displacement control valve 300 depending on the detected results. Then, a discharge quantity of the variable displacement compressor 100 is controlled so that the pressure in the suction chamber 119 to a predetermined value.

FIG. 2 shows a cross-section of a principle part of the variable displacement compressor 100 according to the present embodiment. Herein, the cross section of the variable displacement compressor 100 shown in FIG. 2 shows a cross section of the variable displacement compressor 100 at a position at which the top thereof is slightly rotated toward a near side of the sheet around the driving shaft 106 as compared with the cross section of the variable displacement compressor 100 shown in FIG. 1.

In the cylinder block 101, communication passages 101 c and 101 d communicating with the muffler space 123 and the crank chamber 105 are provided on the downstream side of the check valve 200 in the muffler space 123.

The communication passage 101 c communicates with the muffler space 123 and the communication passage 101 d.

The communication passage 101 d is provided as a part of an insertion hole into which a through bolt 140 is inserted, which communicates with the crank chamber 105. A large flow passage area is secured in a portion of the insertion hole serving as the communication passage 101 d.

At a connecting position with the communication passage 101 c in the muffler space 123, a high-pressure relief valve 250 is arranged. On this account, the muffler space 123 is communicable with the crank chamber 105 through an inner passage (including a space 256 to be described later) of the high-pressure relief valve 250, the communication passage 101 c, and the communication passage 101 d. Herein, the inner passage of the high-pressure relief valve 250, the communication passage 101 c, and the communication passage 101 d serve as a first pressure release passage communicating with the discharge passage and the crank chamber 105. Accordingly, the first pressure release passage is branched from a discharge passage on the downstream side of the check valve 200 in the discharge passage and is connected to the crank chamber 105. Furthermore, the first pressure release passage is positioned radially outward of the cylinder bore 101 a seeing from the driving shaft 106.

FIG. 3 schematically shows a structure of the high-pressure relief valve 250.

The high-pressure relief valve 250 includes a bottomed cylindrical valve housing 251, a valve body 252 arranged in the valve housing 251, a spring 253 urging the valve body 252 in a valve closing direction, a spring guide 254 receiving one end of the spring 253, and an O-ring 255.

At the upper end of the valve housing 251, an inlet port 251 a communicating with the inside and the outside of the valve housing 251 is formed.

At the center of the spring guide 254, an outlet port 254 a communicating with the inside and the outside of the valve housing 251 is formed.

The pressure in the crank chamber 105 is acted on a space 256 at the rear side of the valve body 252 defined by the valve housing 251 and the spring guide 254. On this account, the high-pressure relief valve 250 is opened when the pressure in the muffler space 123 (discharge pressure region) exceeds a predetermined value previously set based on the pressure in the crank chamber 105 and urging force of the spring 253 to discharge the refrigerant in the muffler space 123 into the crank chamber 105 through the first pressure release passage. In other words, the high-pressure relief valve 250 is opened when the pressure on the downstream side of the check valve 200 in the discharge passage exceeds a predetermined value. Herein, the predetermined value is a threshold value for switching open and close operations of the high-pressure relief valve 250, which is previously set to pressure higher than pressure that may possibly occur in a normal air conditioner operating condition. Therefore, the high-pressure relief valve 250 is closed in the normal air conditioner operating condition.

One end side of the high-pressure relief valve 250 to which the O-ring 255 is attached is engaged into the cylinder block 101 and the other end side of which is arranged so as to face to the lid member 122. The high-pressure relief valve 250 is held in the cylinder block 101 by elastic force of the O-ring 255. In order to prevent the high-pressure relief valve 250 from coming out off from an engaging part of the cylinder block 101, a part of the lid member 122 contacts an upper surface of a flange 251 b of the valve housing 251 to restrict movement of the high-pressure relief valve 250.

A description will then be made to an operation of the high-pressure relief valve 250.

In a state in which the variable displacement compressor 100 is in operation and the refrigerant is circulated to the refrigerant circuit of the vehicle air conditioning system (check valve 200 is opened), when the pressure on the discharge pressure region increases to the overpressure, and the pressure in the muffler space 123 exceeds a predetermined value previously set based on the pressure in the crank chamber 105 and the urging force of the spring 253, the high-pressure relief valve 250 is opened to discharge the refrigerant in the muffler space 123 into the crank chamber 105 through the first pressure release passage. Thus, the pressure in the crank chamber 105 is suddenly increased and a pressure difference between the crank chamber 105 and the suction chamber 119 is increased to decrease inclination of the swash plate 107. Thus, a stroke of reciprocating motion of the piston 117 is decreased, resulting in a decrease in a discharge quantity of the variable displacement compressor 100 to a minimum discharge quantity. Therefore, the pressure in the discharge chamber 120 is markedly decreased to thereby avoid the occurrence of the overpressure in the variable displacement compressor 100. At this moment, the check valve 200 closes. However, because the muffler space 123 is located on the downstream side of the check valve 200, refrigerant in the discharge-side refrigerant circuit of the vehicle air conditioning system continuously flows into the crank chamber 105 through the first pressure release passage and migrates to the suction chamber 119 through the gas bleeding passage 128. Herein, the gas bleeding passage 128 serves as the second pressure release passage according to the present invention. In this way, the embodiment enables avoiding not only the occurrence of the overpressure in the discharge chamber 120 (that is, on the upstream side of the check valve 200 in the discharge pressure region) of the variable displacement compressor 100, but also the occurrence of the overpressure in the discharge-side refrigerant circuit (that is, on the downstream side of the check valve 200 in the discharge pressure region) of the vehicle air conditioning system.

Thereafter, when the overpressure on the discharge pressure region is relieved, the high-pressure relief valve 250 closes and the vehicle air conditioning system proceeds to a normal operating state.

According to the present embodiment, since when the pressure in the muffler space 123 exceeds the predetermined value, the first pressure release passage (inner passage of the high-pressure relief valve 250, the communication passage 101 c, and the communication passage 101 d) is opened by the high-pressure relief valve 250 to discharge the high pressure refrigerant into the crank chamber 105 through the first pressure release passage, the embodiment eliminates the necessity of discharging the refrigerant into the air during depressurization.

Further, according to the present embodiment, when the pressure in the muffler space 123 exceeds the predetermined value, the refrigerant on the downstream side of the check valve 200 in the discharge passage is discharged into the crank chamber 105 through the first pressure release passage (inner passage of the high-pressure relief valve 250, the communication passage 101 c, and the communication passage 101 d). Thus, the pressure in the crank chamber 105 is suddenly increased and the discharge quantity of the variable displacement compressor 100 is instantaneously decreased to the minimum discharge quantity, to markedly drop the pressure in the discharge chamber 120, thereby avoiding the occurrence of the overpressure in the discharge chamber 120.

Furthermore, according to the present embodiment, the provision of the first pressure release passage (inner passage of the high-pressure relief valve 250, the communication passage 101 c, and the communication passage 101 d) and the second pressure release passage (gas bleeding passage 128) allows smooth migration of the high pressure refrigerant to the suction chamber 119 through the first pressure release passage, the crank chamber 105, and the second pressure release passage when the pressure in the discharge-side refrigerant circuit increases, for example, to the overpressure. Therefore, it is possible to avoid the occurrence of the overpressure in the discharge-side refrigerant circuit.

Moreover, according to the present embodiment, it is possible to avoid both the occurrence of the overpressure in the discharge chamber 120 (that is, on the upstream side of the check valve 200 in the discharge pressure region) and the occurrence of the overpressure in the discharge-side external refrigerant circuit (that is, on the downstream side of the check valve 200 in the discharge pressure region), and thus, the embodiment enables enhancing the reliability of the vehicle air conditioning system.

Furthermore, according to the present embodiment, at least part of the first pressure release passage (inner passage of the high-pressure relief valve 250, the communication passage 101 c, and the communication passage 101 d) is positioned radially outward of the cylinder bore 101 a seeing from the driving shaft 106. Thus, it is possible to relatively easily form the communication passages 101 c and 101 d used for connection between the muffler space 123 and the crank chamber 105. Additionally, since it is possible to relatively easily provide the high-pressure relief valve 250, the embodiment enables effective manufacture of the variable displacement compressor 100.

Furthermore, according to the present embodiment, a muffler 121 having an extended space is provided between the communication passage 124 and the discharge port 122 a and the high-pressure relief valve 250 is arranged in the extended space (muffler space 123). Since the muffler 121 may serve as a cover for the high-pressure relief valve 250, the embodiment allows reducing damage to the high-pressure relief valve 250 caused from the outside.

Furthermore, according to the present embodiment, the muffler 121 includes the volume part (formed wall 101 b) provided by forming a concavity on an upper surface of the cylinder block 101 and the lid member 122 covering the opening of the volume part. Thus, since it is possible to attach and remove the high-pressure relief valve 250 in a state in which the lid member 122 is detached from the opening of the volume part, the embodiment enables providing the effective operation.

Moreover, according to the present embodiment, a part of an insertion hole into which a through bolt 140 is inserted serves as the communication passage 101 d constituting the first pressure release passage. Since the communication passage 101 d may be continuously or integrally provided at the time of formation of the insertion hole, the embodiment enables simplification of the formation of the first pressure release passage.

FIG. 4 schematically shows a structure of the variable displacement compressor according to a second embodiment of the present invention.

A description will be made to points different from the first embodiment shown in FIGS. 1 to 3.

Whereas in the first embodiment, the gas bleeding passage 128 includes the orifice 103 c, in the second embodiment, the gas bleeding passage 128 includes a low-pressure relief valve 280 in place of the orifice 103 c.

FIG. 5 schematically shows a structure of the low-pressure relief valve 280.

The low-pressure relief valve 280 is arranged in the suction chamber 119 and includes a valve seat forming member 281, a valve body 282, a spring 283, and a valve housing 284.

In the valve seat forming member 281, an inlet port 281 a communicating with the crank chamber 105 through the space 127, etc. and a valve seat 281 b are provided.

The valve seat forming member 281 includes a flange 281 c. The flange 281 c is engaged into a through hole previously formed in the valve plate 103, which is clamped and held between a suction valve forming body 150 and a discharge valve forming body 160, each being arranged adjacent to the valve plate 103.

The valve body 282 includes a sealing surface seated on the valve seat 281 b, and closing the inlet port 281 a and a cylindrical outer peripheral surface.

In the valve body 282, an orifice 282 a is formed so that the crank chamber 105 communicate at all times with the suction chamber 119 when the valve body 282 is seated on the valve seat 281 b.

The spring 283 urges the valve body 282 toward the valve seat 281 b.

The valve housing 284 has a bottomed cylindrical shape receives at the inside of which one end of the spring 283, and slidably supports the cylindrical outer peripheral surface of the valve body 282. Further, the valve housing 284 has a plurality of outlet ports 284 a formed on the cylindrical peripheral surface therethrough and communicating with the suction chamber 119.

Further, in the valve housing 284, a communication hole 284 b is formed so that the pressure in the suction chamber 119 acts on a space 285 at the rear side of the valve body 282.

Thus, the low-pressure relief valve 280 is opened when a pressure difference between the crank chamber 105 and the suction chamber 119 exceeds a predetermined value previously set based on the urging force of the sparing 283 to discharge in large quantities the refrigerant in the crank chamber 105 into the suction chamber 119 through the gas bleeding passage 128 (second pressure release passage). Herein, the predetermined value is a threshold value for switching open and close operations of the low-pressure relief valve 280, and is previously set to a value greater than the pressure difference between the crank chamber 105 and the suction chamber 119, which may possibly occur during normal pressure control of the crank chamber 105. Therefore, the low-pressure relief valve 280 is closed in a normal air conditioner operating condition.

A description will then be made to an operation of the high-pressure relief valve 250 and the low-pressure relief valve 280 according to present embodiment.

In a state in which the variable displacement compressor 100 is in operation and refrigerant is circulated to the refrigerant circuit of the vehicle air conditioning system (check valve 200 is opened), when the pressure on the discharge pressure region increases to the overpressure and the pressure in the muffler 123 exceeds a predetermined value previously set based on the pressure in the crank chamber 105 and the urging force of the spring 253, the high-pressure relief valve 250 is opened to discharge the refrigerant in the muffler space 123 into the crank chamber 105 through the first pressure release passage. Thus, the pressure in the crank chamber 105 is suddenly increased and a pressure difference between the crank chamber 105 and the suction chamber 119 is increased, to thereby decrease inclination of the swash plate 107 and a stroke of reciprocating motion of the piston 117. Therefore, a discharge quantity of the variable displacement compressor 100 is decreased to a minimum discharge quantity, to markedly drop the pressure in the discharge chamber 120, thereby avoiding the occurrence of the overpressure in the variable displacement compressor 100.

Further, when the pressure difference between the crank chamber 105 and the suction chamber 119 exceeds the predetermined value previously set based on the urging force of the spring 283, the low-pressure relief valve 280 is opened to discharge the refrigerant in the crank chamber 105 into the suction chamber 119 through the gas bleeding passage 128 (second pressure release passage). At this moment, the check valve 200 closes. However, since the muffler space 123 is located on the downstream side of the check valve 200, the refrigerant in the discharge-side refrigerant circuit of the vehicle air conditioning system continuously flows into the crank chamber 105 and migrates to the suction chamber 119 through the gas bleeding passage 128 (second pressure release passage). In this way, the embodiment enables avoiding not only the occurrence of the overpressure in the discharge chamber 120 (that is, on the upstream side of the check valve 200 in the discharge pressure region) of the variable displacement compressor 100, but also the occurrence of the overpressure in the discharge-side refrigerant circuit (that is, on the downstream side of the check valve 200 in the discharge pressure region) of the vehicle air conditioning system.

According to the present embodiment, the low-pressure relief valve 280 which opens the second pressure release passage when a pressure difference between the crank chamber 105 and the suction chamber 119 exceeds a predetermined value is provided in the second pressure release passage (gas bleeding passage 128). Thus, since it is possible to migrate a large amount of refrigerant to the suction chamber 119 while suppressing an excessive increase in the pressure difference between the crank chamber 105 and the suction chamber 119, the embodiment enables prompt relief of the overpressure on the discharge pressure region.

In the present embodiment, a passage serving as the second pressure release passage is only the gas bleeding passage 128, not necessarily limited thereto, for example, a new second pressure release passage having the low-pressure relief valve 280 may be provided, apart from the gas bleeding passage 128. That is, the second pressure release passage may have plural passages.

FIG. 6 schematically shows a structure of the variable displacement compressor according to a third embodiment of the present invention. FIG. 7 schematically shows a structure of a high-pressure relief valve according to the present embodiment.

A description will be made to points different from the first embodiment shown in FIGS. 1 to 3.

In the first embodiment, the high-pressure relief valve 250 is opened when the pressure in the muffler space 123 (discharge pressure region) exceeds the predetermined value previously set based on the pressure in the crank chamber 105 and the urging force of the spring 253. In the third embodiment, the high-pressure relief 260 is opened when pressure in the muffler space 123 (discharge pressure region) exceeds a predetermined value previously set based on urging force of the spring 263.

The high-pressure relief valve 260 includes a valve housing 261, a diaphragm 262, a spring 263, a spring guide 264 disposed between the diaphragm 262 and one end of the spring 263, a spring guide 265 disposed between the other end of the spring 263 and the valve housing 261, and an O-ring 266.

The valve housing 261 includes a first housing member 261 a constituting one end side of the valve housing 261 and a second housing member 261 b constituting the other end side thereof. In the first housing member 261 a, an inlet port 261 c communicating with the muffler space 123, an outlet port 261 d communicating with the crank chamber 105 through the communicating passages 101 c and 101 d, and a valve seat 261 e on which the diaphragm 262 seats are formed.

The diaphragm 262 receives at one end face the pressure in the muffler space 123. A space defined by the diaphragm 262 and the second housing member 261 b of the valve housing 261 is held at negative pressure, and the spring 263 urges the diaphragm 262 toward the valve seat.

Accordingly, the high-pressure relief valve 260 is opened and closed when the diaphragm 262 displacing in response to the pressure in the muffler space 123 (discharge pressure region) seats to and separates from the valve seat 261 e. When the pressure in the muffler space 123 (discharge pressure region) exceeds a predetermined value, the high-pressure relief valve 260 is opened to discharge the refrigerant in the muffler space 123 into the crank space 105 through the first pressure release passage.

In this connection, the first housing member 261 a and the second housing member 261 b of the valve housing 261 are bonded by welding together their flanges 261 f while the diaphragm 262 is sandwiched therebetween. Herein, the first housing member 261 a and the second housing member 261 b are made of the same material (for example, a stainless material).

One end side (first housing member 261 a) of the high-pressure relief valve 260 to which the O-ring 266 is attached is engaged into the cylinder block 101 and the other end side (second housing member 261 b) thereof is arranged so as to face to the lid member 122. The high-pressure relief valve 260 is held in the cylinder block 101 by elastic force of the O-ring 266. Further, in order for the high-pressure relief valve 260 to prevent the valve from coming out off from an engaging part of the cylinder block 101, a part of the lid member 122 contacts an upper surface of the flange 261 f of the valve housing 261. That is, the high-pressure relief valve 260 is clamped, at the flange 261 f of the valve housing 261, by the cylinder block 101 and the lid member 122.

According to the present embodiment, since the high-pressure relief valve 260 is opened when the pressure in the muffler space 123 (discharge pressure region) exceeds the predetermined value previously set based on the urging force of the spring 263, an operation of the valve may be carried out in correctly response to the pressure in the muffler space 123 (discharge pressure region) without being scarcely influenced by the pressure in the crank chamber 105. Consequently, the embodiment enables enhancing the reliability of the variable displacement compressor 100 and the vehicle air conditioning system adopting the variable displacement compressor.

Furthermore, according to the present embodiment, the high-pressure relief valve 260 is clamped by the cylinder block 101 and the lid member 122. This, since the embodiment eliminates the need for a fixing member for fixing the high-pressure relief valve 260 to the cylinder block 101, the embodiment allows implementing the improvement in attachability and cost reduction.

In the high-pressure relief valve 260, the diaphragm 262 is used as a pressure-sensitive member, not necessarily limited thereto, for example, a bellows may be used alternatively as the pressure-sensitive member.

In the high-pressure relief valve 260, the diaphragm 262 functions as a valve body, not necessarily limited thereto, for example, the high-pressure relief valve 260 may include a valve body, together with or in place of the diaphragm 262.

FIG. 8 schematically shows a structure of a variable displacement compressor according to a fourth embodiment of the present invention.

A description will be made to points different from the present embodiment shown in FIGS. 1 to 3.

In the first embodiment, the muffler 121 is provided in the periphery of the cylinder block 101, in the fourth embodiment, the muffler 121 is not provided.

As shown in FIG. 8, the cylinder head 104 includes a discharge port 104 c and a communication passage 104 d outwardly extending from the discharge chamber 120 toward the discharge port 104 c and perpendicularly extending with respect to a shaft direction of the driving shaft 106. Herein, a function of the discharge passage of the present invention is implemented by the discharge port 104 c and the communication passage 104 d.

In the middle of the communication passage 104 d, the check valve 200 is provided.

In the cylinder head 104, a part of the communication passage 130 communicating with the communication passage 104 d on the downstream side of the check valve 200 is provided.

In the cylinder head 104, the communication passage 130 branches from the communication passage 104 d on the downstream side of the check valve 200, extends in parallel with the driving shaft 106, and communicates with an inlet port of the high-pressure relief valve 270 provided in the cylinder block 101.

One end side of the high-pressure relief valve 270 to which the O-ring is attached engages into the cylinder block 101 and the other end side of which outwardly protrudes from the cylinder block 101. In this connection, the high-pressure relief valve 270 has the same structure as that of the high-pressure relief valve 260, but the high-pressure relief valve 270 outwardly protrudes from the cylinder block 101. Thus, the O-ring for sealing off from the air is added and retained by a snap ring 132.

An outlet port of the high-pressure relief valve 270 communicates with the crank chamber 105 through the communication passages 101 c and 101 d.

Accordingly, the first pressure release passage communicating with the communication passage 104 d and the crank passage 105 includes the communication passage 130, an inner passage of the high-pressure relief valve 270, and the communication passages 101 c and 101 d.

According to the present embodiment, in the cylinder head 104, the communication passage 130 branches from the communication passage 104 d on the downstream side of the check valve 200, extends in parallel with the driving shaft 106, passes through the valve plate 103, and communicates with an inlet port of the high-pressure relief valve 270 provided in the cylinder block 101. Hence, it is possible to easily form the communication passage 130, as with the forming the insertion hole for the through bolt 140.

In the aforementioned first to fourth embodiments, the outlet port of the high-pressure relief valve is connected to the crank chamber 105 via a part of the insertion hole (communication passage 101 d) for the through bolt 140. Alternatively, the outlet port may be directly connected to the crank chamber 105 not via the insertion hole for the through bolt 140.

Additionally, in the aforementioned first to fourth embodiments, it is possible to arrange a filter, at the upstream side of the high-pressure relief valve in the first pressure release passage, or at the discharge-side refrigerant circuit side rather than a branching position of the first pressure release passage in the discharge passage. Thus, since when the high-pressure relief valve is opened, the filter may remove foreign matters invaded in the discharge-side refrigerant circuit, the embodiment enables reducing a risk of deteriorating the durability caused by the foreign matters.

In the variable displacement compressor 100 according to the aforementioned first to fourth embodiments, the discharge chamber 120 is annularly arranged radially outward of the suction chamber 119, not necessarily limited thereto. In contrast to the arrangement of the discharge chamber and the suction chamber in the aforementioned first to fourth embodiments, the suction chamber may be annularly arranged radially outward of the discharge chamber.

Further, in the second embodiment, the low-pressure relief valve 280 is arranged in the suction chamber 119. In contrast to the arrangement of the discharge chamber and the suction chamber in the aforementioned second embodiment, when the suction chamber is annularly arranged radially outward of the discharge chamber, it is preferable to arrange the low-pressure relief valve 280 at the cylinder block 101 side.

Moreover, the variable displacement compressor 100 according to the aforementioned first to fourth embodiments may be a variable displacement compressor equipped with an electromagnetic clutch or a clutchless compressor, etc. In addition, an external driving source driving the variable displacement compressor 100 may be an automobile engine and a motor, etc.

Since the variable displacement compressor 100 according to the aforementioned first to fourth embodiments discharges the refrigerant into the crank chamber 105 without discharging the refrigerant into the air when avoiding the occurrence of the overpressure in the discharge pressure region, this structure is especially suitable for a variable displacement compressor adopting flammable refrigerant.

REFERENCE SIGNS LIST

-   -   100 Variable displacement compressor     -   101 Cylinder block     -   101 a Cylinder bore     -   101 b Formed wall     -   101 c, 101 d Communication passage     -   102 Front housing     -   103 Valve plate     -   103 c Orifice     -   104 Cylinder head     -   104 a Suction port     -   104 b Communication passage     -   104 c Discharge port     -   104 d Communication passage     -   105 Crank chamber     -   106 Driving shaft     -   107 Swash plate     -   117 Piston     -   119 Suction chamber     -   120 Discharge chamber     -   121 Muffler     -   122 Lid member     -   122 a Discharge port     -   123 Muffler space     -   124 Communication passage     -   125 Gas supplying passage     -   127 Space     -   128 Gas bleeding passage     -   130 Displacement control valve     -   140 Through bolt     -   150 Suction valve forming body     -   160 Discharge valve forming body     -   200 Check valve     -   250,260,270 High-pressure relief valve     -   280 Low-pressure relief valve 

1. A variable displacement compressor comprising: a housing including a plurality of cylinder bores formed in parallel with one another around a shaft, a crank chamber provided at the front thereof, a suction chamber and a discharge chamber provided at the rear thereof, a discharge passage connecting the discharge chamber to a discharge-side external refrigerant circuit, and a suction passage connecting the suction chamber to a suction-side external refrigerant circuit; a piston inserted into the cylinder bore to reciprocate therein and compressing refrigerant drawn from the suction chamber to discharge the refrigerant into the discharge chamber; a driving shaft rotatably supported in the housing; a conversion mechanism including a swash plate of which inclination is changeable, the swash plate being arranged in the crank chamber and converting a rotary motion of the driving shaft into a reciprocating motion of the piston; and a displacement control valve changing the inclination of the swash plate by controlling pressure in the crank chamber to change a stroke of the reciprocating motion of the piston, wherein the housing includes a first pressure release passage branched from the discharge passage and connected to the crank chamber, and a second pressure release passage connecting the crank chamber to the suction chamber, wherein a check valve that suppresses a backward flow of the refrigerant from the discharge-side external refrigerant circuit to the discharge chamber is provided in the discharge passage on an upstream side of a branching position at which the first pressure release passage branches off, and wherein a high-pressure relief valve that opens the first pressure release passage when pressure in the discharge passage on a downstream side of the check valve exceeds a predetermined value is provided in the first pressure release passage.
 2. The variable displacement compressor according to claim 1, wherein at least part of the first pressure release passage is positioned radially outward of the cylinder bore seeing from the driving shaft, and the high-pressure relief valve is arranged at the at least part of the first pressure release passage.
 3. The variable displacement compressor according to claim 1, wherein the discharge passage includes a muffler having an extended space, and the high-pressure relief valve is arranged in the expanded space.
 4. The variable displacement compressor according to claim 3, wherein the muffler includes a volume part which is a part of the housing and is provided by forming a concavity on an external surface of a cylinder block in which the cylinder bore is formed, and a lid member which is a part of the housing and covers an opening of the volume part.
 5. The variable displacement compressor according to claim 4, wherein the high-pressure relief valve is clamped by the cylinder block and the lid member.
 6. The variable displacement compressor according to claim 1, wherein a low-pressure relief valve that opens the second pressure release passage when a pressure difference between the crank chamber and the suction chamber exceeds a predetermined value is provided in the second pressure release passage. 